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Monday, 23 April 2012

Altium Designer Supplier Cost Rounding Error

Here's an annoying bug in Altium Designer Summer '09. Altium Designer allows you to link your schematic library components with a supplier's product inventory such as Digi-Key or Farnell. When you generate a BOM the supplier cost is retrieved from the supplier website and pumped into an Excel spreadsheet. Well that is the idea.

If you have components costing less than 1p and presumably 1 cent then they are rounded down to 0p. This is pretty unhelpful if you want to know the total BOM cost.

The workaround is to use the "Supplier Subtotal 1" field instead of "Supplier Unit Price 1" field and to set a Production Quantity of say 10, or 100 off. This forces Altium to multiply the unit cost by the quantity per board and by the production quantity before rounding! Typically this values is more than 1p and you can get an accurate per board BOM cost by dividing the sum of subtotals by the production quantity.

Of course, this is not perfect, since changing the production quantity can push you into a different supplier price bracket. I'm probably not the first person to find this bug, but because Altium developers keep their bug reporting system private I cannot be sure! I hope to log a bug report as soon as I'm granted a log in to Altium Live.

Hopefully this workaround will be useful to others struggling to calculate a BOM cost for their design.